Electbic furnace



'Jul 21. 1925.

A. RUCKSTAHL ELEM-R10 FURNACE Filed May 11. 1922 5 Sheets-Sheet 1 July 21, 1925.

A. RUCKSTAHL' I ELECTRIC FURNACE 5' Sheets-Sheet 2 Filed May 11. 1922 Guam,

A. RUCKSTAHL ELECTRIC FURNACE 5 Sheets-Sheet 5 Filed May 11. 1922 lllllllllll m.

I 2. e I

July 2 925. 1,547,000

A. RUCKSTAHL ELEG IRIG FURNACE ilq May 11. 1922 5 Sheets-Sheet 4 I M12922: 4 j

Patented July 21, 1925.

UNITED STATES ALFRED nucnsrnnn, or nnrnorr, mcnisnn.

morale rusum Application mac May '11,

To all whom "it may concern:

Be it known that I, Armn Rucxsrerm a citizen of the United States of America, residing at Detroit, in the county of Wayne and State of Michigan, hcve'invented certain new and useful Improvements in Electric Furnaces, of which the following is a specification, reference being had therein to the accompanying drawings.

This invention relates to electric furnaces suitable for the heat treatment of large cheats at high temperatures. p

it is the o jeot of the invention to provide an arran entof the. resistors by which changes and substitutions ma readily be made without the necessity o cooling down the furnacea'nd with the minimum removal of parts. The current'practice in large furnaces heated byelectric resistance elements, is to arrange si -series oifiirisulating supports of refractory material project ng from the side walls pf-thefiurnace at points near the top ami bottomfloi the sidewalls. U 11 these so ports is looped, a continuous ribbon of an a lloy having li'igh electric resistance in a sinuous path with the portions of the ribbons between the refractory 'supports substantially vertical. This""co ntinuous ribbon is made to extend from one end of the furnace to the other upon the opposite side walls of the furnaceim'd' if; any break occurs, it is necessary to allow the-furnace to cool down sotheta workman may' '.enter the and remove the entireheating element. This oration requires considerable time and 1aor and duringthe period of replacement the furnace is out of use.

It has been proposed to provide resistence conductors carried b refractory plates extending longitudinal y through the furnace and supported by rall sections mounted in grooves in the bricking of the furnace arch and sides whereby'the supports may be shifted lon -itudi'nally' of the furnace. In

' this ceset e resistance conductors 'itre of continuous length throughout the longitudi} nal extent 'of'the furnace andwhenever it is necessarvto replace eliciting element, the front wall or rear wall of It a furnace must be removed to permit -the withdrawal of the resistance elements with their suports.

p Another familiar type of furnace has the resistance element in the form of a, heavy wire usually. about a uarter of an inc square bent to forrn a airpin-shapcd ele- 1922. Serial No. 560,186.

rnent of the length-of the furnace inserted in the furnace wells-with the elenient running from front to back. In replacing such elements the furnace must be cooled and the length of the furnace in ractice is' limited to about six feet dueto t e bendin of the units in the fiunace. ,It isve difiiculti to remove burnt out units and t ore is considerablc loss of heat due to the form of connection made necessary by the hairpinshnpe- Inthe development of the electric furnace, it has been found desirable to localize heating temperatures to 'suit particularqheat conditions. Where the samefurnace is to be used with diilcrcntmaterials-, it dosirable that the heat conditions inaytbemade variable invarious portions of-tlie furnace. "Ihe present methods of=arran 'ng the heat mg elements make' l'this locahzed'variatibn of tem erature extremdy-difiicflt iif-"no't im Ossi 7,; J: l; IN-.2-

t is the object of the present invention to provide a heatingclement or unit of the metallic resistor type which may be inserted through the side walls of the furnaoe sq that the heating units can beremoved or interchanged without dismantling the furnace and without the' necessity of'fcooling down the'furnace I 'A further ob'ect of the invention it to providef ahea' madepf a'; suitable ribbon" or a wireesigned to "allowawide range of-variatioii' in heat so-thatfh'y the substitution of one unit for another, variations in localized heat conditions may be readily made. W I

A further object of the inventiionis to provide a; form of heating element in which the necessary; length .of resistance material may be utilized transversely of the furnace so that the heat may b'e applied from overhead'ina furnace relatively wider and lower than those at present in use. The necessity for the relatively greater height required in the present type to accomodate a suifioient len h of resistance'material will be obviate by the'use ofa form of resistor element in wh ch the necessary length of resistance material may be arranged -transversely of the furnace instead of vertically upon the side walls.

A still further object of the invention is to provide a heating unit which shall be convenient to handle and of relatively cheap construction.

I obtain these andother objects by the construction illustrated in the accompanyingrdrawings, in wh1 ch igure 1 is an end elevation, parts being shown in section, of one form of furnace, containing a preferred embodiment of my device; A

Fig. 2 is a fragmentary perspective view illustrating :a removable resistor element;

Fig. 3 is a longitudinal section of'thc type of furnace illustrated in Fig. 1*;

Fig. 4 is a horizontal section of a portion of another type of furnace illustrating a. modified form .of construction;

Fig. 5 is a, vertical section through the same form of furnace;

Fig.5 is a fragmentary perspective view showing the type of furnace shown in Figs. 4 and 5;

F 7 is a hagmentary view showing a modi cation;

Fig. 8'is 11 pers ective viewof a modified formofresistor ement;

-Fig. 9 is a longitudinahsection of a. still iurther modification;

Fi t-105s a transverse sec 'onthrough the modilication illustrated in Fig. 9-;

'Fi 11 is-a; fisgmentarg view showing a de .ofconstnuction; an

Fig. 12 is a fragmentary section of a modification.

In Fig.1 there is illustrated a. conventional form of iurnace comprisin a brick wail-l1 surrounded by a-metal sl1i d--2-a-ncl having an inner lining?) of .fire brick or other suitable::reiracteig1 materiah- At frequent intervals alonge side will of the furnace passageways 4 are-provided of a. size sufiicientrto-permit;,the insertion and removal therethroughi of resistonceelements or-units 5. Thesexelements-domprise side bars -6 preferably of an alloy-highly resistant to heat and oxidation as for example, an alloy of nickel and chromium, or of nickel, chromium and iron, and it should have'substnntiallythe s'ameco-efiicient of en ansion as the heating. means. v The speci c alloy forms no-par-t of the present invention and may be varied tosuit conditions. At the ends, the "side bars 6 are separated by refractory members 7 longitudinally -per-forated for the reception of rods 8. The rods are'provide'd with nuts 9 between which are clamped the bars -6,. At the centxnl-portion of the element is a channelmember having end flanges l1 and side flanges 12 :and 13. bolted, riveted or welded at 14 to the side bars 6. Lying within the channel member 10 is a-bar of refractory material 15' having a series of partition members 16' upon its ":Ulle! surface. The bars 7 have partition rZcinber-s 17 between which are arranged the looped end-portions 18 of the resistance llllilOllS 19 of a suitable alloy. There are about twice as many partition members 16 the arrangement of the doors inas there are members 17 the members 16 separati arallel portions of adjacent ribbons, u n c the members 17 act to separate adjacent loops while permitting longitudinal movement of the loops due to their contraction'and expansion under the influence of heat. The sinuously arranged ribbon supported by the transverse refractory elements 7 an 15 has its terminals 19 and 20 extending longitudinally beyond the end of the frame of the unit 5 for a sufficient distance that when the unit .is set in position within the iurnace the :ends of the -resistor ribbon will extend outward beyond the outer wall .of the furnace.

Recessed bricks 21 will 'be used .to fill the passageways 4 and upon the outside of the furnace, brackets. 22 will sup ort asbestos lates 23 which may be secure in place as y nuts 24.

It will be seen'that the resistor unit just described may be madeoef any convenient width and length for insertion and removal and it will also (beevident that by varying the number of turns or loops-of the resistance ribbons, the heating conditions may be made difi'eient-fora-difierent units It will thus beflpcssible'to remove-a broken element or to substitute-element listings clifierent resistance or a difiere'nt monnt-goflieatin surface without dismantling K he furnace an without the-necessity of waiting for the furnace to-cool down. 9 15, I

In Figs. 4 to'8 inclusive, a modified form of ,furnaceemhodyingthe present invention has been illustrated. In :this .modification, the furnace-is made in the form of a rim" or annulus 25 containing a.chamber.2 wit in which a carriage?! is-mpunted-forzrotation. A centralsupporting 2S.is mounted in an iuplqpr bearing 29 an'd a lower bearing 30. e central'portion of the shaft is screwthreadecl as at 311m receive-an adjusting but 32 by-nieanspf .which a collar 33 ma be raised or lowered Carriedbythe co ar'33.-are suspension rodS-Mattached at their lower ends to the supportingbcams fio,

the outer ends of which .carry the annular carriage 27. liVh eels 36 enga 'ing a track 37 may be used as an additiond-l supporting means for the outer. end of the beams 35 if desired. Theannular'chamber 26 will be lined with a suitable refractory material 38 and sand seals 39 and 40 are provided at the joints between the lower-edges'of the rotary carriage 27 'and theolon'er edge of the refractory lining 38. a

Arranged transverse y oi the annular chamber 26 and substantially radially of the furnace are a series of resistance elements 41 which in the present instance are shown as consisting of arches. Each arch consists of a sinuous resistance conductor having the curved ends substantially in line with each other at each end of 'the arch, the 'nietal forming the resistance conductor being wider in its vertical dimensions than transversely. Preferably these elements will consist of castings though it will be evident that they may be constructed of a fiat ribbon first bent in n. configuration similar to that shown in Fig. 8 and then bent to form anarch in which the transverse portions of the ribbon will be substantially arallel with their greatest width in substantially vertical planes.

The alloy used for the resistance elements has sufficient strength even at high temperatures to support its own weight without injurious sagging and in cases where the width of the furnace is not too at the heating element may be constructe as s own in Fig. 8. The material may be in the form of a fiat ribbon 42 having its runs substantially parallel with the curved ends of the loops substantially in line to rest upon suitab e supports at opposite sides of the chamber.

It will be 0 vious that instead of a rolled ribbon the material may be cast into a similar form if desired. With either form of re sistance element, whether arched or straight, the terminal members 43 will be longenou h to extend beyond the outer wall and t 1e passageways 44 will then be filled with bricks 45, some ofwhich may be perforated as indicated at 46 to ermit the terminals 43 to pass through an insulating body with the minimum of open space. Asbestos plates 47 perforated at 48 for the passage of the terminals 43, will cover the outer ends of the bricked in passageways as a further insulation.

The furnace will preferably have a jacket 49 of sheet metal.

In Figs 1, 2 .3 .5 and 6; the supports for. the-:ends of the resistor elements are shown as formed by the ends of projecting portions 50 of the: refractory lining of the side walls of the chamber.

In Fig. 7 the end of the resistor element is shown as resting within a recess 51 in'the side wall, the projecting portion 50 shown in Fig. 1, be omitted with the consequent lengthening o the supporting framework 5 of a resistor member. This has the advert tageof securing a reator length of resistance material and tiere is no projecting refractory material to screen an portion of the chamber from the heat of t 1e resistor.

.Another modification of the-invention is illustrated in Figs. 9, 10 and 11. In the furnace shown in these figures, the removable resistance elements comprise side members 52 of a metallic alloy highly resistant to heat and oxidation, the side members 52 being connected by transverse braces 53 of the same material. At intervals the side members 52 are formed with webs 54 are ranged in pairs to receive therebetween transverse bars 55 of a refractory material of time so that the furnace was out of such as alundum. As shown, these bars have perforations 56 which in the present instance are stag cred, and through these perforations coi ed spirals of resistance wire are threaded. In this manner a large heating surface is exposedand by a roper arrangement of the connections of die terminals of the resistor elements, the electrical conditions and hence the heat conditions may be varied at the will of the operator.

The heating elements are shown as arranged abor'e and below the chamber 57 so that heat may be applied from overhead or underneath to material supported upon the floor 58, which will be of an alloy similar to that from which the bars are made. This design is especially applicable to small furnaces though it will be evident that the form of resistor element shown in this modification may be applied equally well to the type of furnace shown in Figs. 4c, 5 and 6 or to the type .of furnaoe'shown in Figs. 1 and 3. It will also be evident that the double arrangement of heaters above and beneath the material tube treated may be used in either of the other types of furnaces shown as well as in the type illustrated in Fig. 9.

stantially vertical along the side walls of;

the furnace. A break occurred within the furnace, and in order to replace the element, it'was necessary to allow the furnace to cool. down to a. item eratnre at which a workman could craw into thcfurnace to disconnect the metallic ribbonfrom its supports. In spite of the provision of an artificial su ply of air, it was possible to work withint e furnace for only a short period use fora period of from eight to ten days. The cost of a new resistor element'was a proximately two thousand eight hundred c ollars. After the repair had been made,the furnace was in use only a short timeuntil another break occurred whereupon the entire process had to be repeated at substantially the same cost, with the furnace out of commission for another period of from eight to ten days.

If this furnace had been equipped with resistors elements of any of the types shown in the present application, the break could readily have been located by applying testing: instruments to the exposed terminals and a new element could have been inserted are supported-in doni of expansion arrangement of resistance material enables the operator to vary the heating conditions in a furnace to suit-various operations requiring different heat treatment. This is practicallv impossible in furnaces now in the winding consists of a conuse wherein tinuous ribbon, the replacement of which requires an excessive amount of time and expenditure of a considerable sum of money.

Another advantage of the present invention is that theheating elements'arc located above the material being treated where danger "of accidental contact is reduced to a minimum 5 the-type of furnace in which the-heating elements are arranged vertically alo q the side walls, the material being movedin o'ancl out'of t-he-fiirnace is'likelv to-be brought into injurious contact with the heating elements. liurthermore, with the overhead arrangement of the heating elements the furnace ;hamber maybe made of less height and the heatinfi' elements will extend entirely across the wor z being treated so, that, the heat jwill be more uniformly applied. that: where "the elements are arranged in the sides of the chamber.

Another important advantage of the presout inventionis that the resistance elements a'ma'rfner permitting reef and contraction. In the type offurnace in which the resistance ele ments are made in the'form of square rods frequently requires of hairpin-shape supported horizontally within the grooves in the side wall or upon supporting brackets. if friction occurs at any point, as the resistor is heated, instead of the element moving freely longitudinally, it, will warp and bow outward from its support or inward against the wall. When the element is permitted to cool down it will not rcsume'its original shape, but when it is reheated the warping action will continue until the element either comes into contact with another element to form a short circuit or the element will extend into the path of the material, 'or 'it will come into contact withthc, furnace wall and become fused thereto so that finally it will be necessary to replace the element and this that the element be chiselled away from the points with which it"lies in contact. l'Vhen it is remembered that'this replacement necessitates cooling down the -furnace ato permit -a workman to enter and that the workman must :p'r-

form his labo; 5 within a confined-space under bad operating conditions, the advantage of being able to remove the heating-element in g to make repairs uponiadefective elemen which has been taken-out.

Since the supporting framework is made of an alloy having substantially the saline co-elficient of expansion as-thatofithe resista-nec alloy used 'for the heating ribbons or other resistor elements, the expansion of the alloy of the resistors will bra-accompanied by almost equal expansion of the 10 'tudinal members of the frame. There Wilflthus be but little need for relative movement between the refractory supports and the resister elements. The framework lengthens, carrying the supports a art concurrently with the lengthening of. emesistanc alloy and there will be littleor mo buckling ofcthe elements. Certain featurcs 'of constnuotion illustrated but not claimed'hereimsre' sham and claimed in my co-pending applications Serial Numbers 560,187 and -560,188,rfiled May11,1922.

It will be obvious that many other-changes and modifications maybe made in-'ztheprac-; tice of my invention'without' departing from its principles or sacrificing an of its advantages. I do not theretore-u to the specific detailsherein'di'sblo'sedQbut desire to claim the invention in'anyoi its forms'or modifications within the legitimate and valid scope ofthe appendedclaims,

I claim: v v

1. In an electric furnace, avhereimthe rfnrnace walls have aiming-of refraotory'inmrial, with one of said walls-havinganiopenin" for the admission-of the material'or antibe subjected-to furnace treatment, said O cles to I furnace having another of its mansion-med with a passageway of a size to permit inser-i tion and removal bodily of a =resistor'rmit, said furnace having a support for the re sistor unit when the latter is in positioni-for active service, and a. resistor umt-havin' a form and dimensions to be supportedavit in the furnace and be movable through such passageway, the movement of thc resistor unitto and from its service positionbeing-iri directions substantially transverseto the direction of axis of such admission opening.

2. 'An electric furnace as in claim 1- char acterized in'that the'resistor unit includes a metallic frame ands current-carrying-conducting element insulated from each other to permit the frame to support the conductor in service position, the conductor and frame being movable to and from-service position as a. unit.

3. An electric furnace as in claim 1 charto bodimitell ltlt :a form and dimensions 4. An electric furnace es in claim 1 characterized in that the resistor unit is in the form of a metallic frame carrying a plurality of spaced insulating elements, said elements having a plurality of individual depressions arranged successively in the direction of length of the element, and a currentcarrying conductor supported within depressions of the insulating elements, whereby the conductor may be given desired flight arrangements within the unit, said frame, insulating elements and conductor being movable to and from service position as a unit.

5. An electric furnace as in claim 1 characterized in that the resistor unit includes a. metallic frame and a current'carrying con ductor insulated from each other to permit the frame to support the conductor in scrvice position, said metallic frame and con ductor having substantially similar co-eliicient of expansion characteristics, said frame and conductor being movable to and from service position as a. unit.

6. In a furnace for'heat-treatment activities, a treatment chamber for the articles or material to be treated, and means for producing the treatment temperatures within such chambelgsaid means including an electric circuit of the non-arcing type. said circuit including a. succession of individual heating units combinedly connected to complete the circuit and individually removable during periods when the material-admission opening to the chamber is closed and in a direction to cross the inner plane of a. chamber wall to permit substitution of units.

7. A. furnace as in claim 6 characterized in that the units are arranged in series relation within the circuit.

8. In an electric furnace. wherein the furnace walls 'having a lining of refractory material, with one of said walls having an opening for the admission of the material or articles tobe subjected to furnace treatment, said furnace having a plurality of passageways each of a size to permit insertion and removal bodily of a resistor unit, and a plurality of resistor units each having to be supported within the furnace and be movable through one of such passageways, the movement of a resistor unit to and from its service position 'bein in directions substantially transverse to tiie direction of axis of such admission opening, sald furnace having supporting mined value,

means for the resistor units when in service sition.

9. A furnace as in claim 8, characterized in that the resistor units are combinedly connected to complete a circuit of non-arcing characteristic within the chamber.

10. A furnace as in claim 8 characterized in that the resistor units are arranged in series relation within the circuit.

11. A furnace as in claim 8 characterized in that the resistor units are combinedly connected to complete a series relation within the temperature-producing circuit, substitutiou of individual units permitting control of the heating characteristics of the circuit.

12. A furnace as in claim 8 characterized in that the resistor units are combinedly connected to complete the temperature-producing circuit and individually removable to permit substitution of units within-thacircuit, the circuit connection of un ts being outside of the furnace walls with the circuit completed by the positioning of units in service position. a e 1' r 13. A furnace as in claim 6 characterized in that each heating unit is formed to produce a heating characteristicyof predeterthe relative arrangement of the heating units within the circuit determining the zonal characteristics of theitcmperzitures of thechamben z 14:. A furnace as in claim 8 characterized in that each resistor unit is ofpredetermined heat-producing characteristic, the relative arrangement of units determining the zonal.

characteristics of the temperatures of the chamber.

15. A furnace as in claim 8 characterized in that each resistor unit is of predetermined heat-producing c iaracteristic within the circuit, the position of the passageways being such as to permit a relative arrangement of the resistor units to set up predetermined iemperature characteristics within the cham 16. A heating element for an electric fur nace comprising a supporting framework carrying transverse refractory insulating members at each end and at the central portion thereof, said insulating members being provided with partition portions for an elec :tric resistance member carried by said insu latmg members,

said resistance member comprising a series of substantially parallel portions separated substantially midway of their length by the partition portions of the centrally located insulating member.

17 A heating element for an electric furnace, said element havin a supporting framework, said frameworli having refractory insulating members at each end, and an electric resistance member having a. series of substantially arallel portions supported at their ends upon said refractory insulatill ing members, said electric resistance member and the side members of the supporting.

2 heat and oxidation, refractory insulating members carried by said framework, and an electric resistance member comprising a strip of ribbon supported by said refractory insulating members, the framework and resistance member having sabstamtially the same co-efiicient of expansion.

19. As a means for preventin the bnckling of' an electric resistance mem er in an electric= furnace, insulating supporting members carrying said resistance member, and a supporting element for said insulating members arranged substantially parallel with said electric resistance member and exposed to the heat thereof, said supporting element and said resistance member having siibstantially the same co-eflicient oi expansion. I

p 20. 'As a means for producing variable heat conditions within thetreatment chamber of a furnace operatingnnder high temperatnre conditiona -meansfor producing the treatment temperatures within the'chamber, said means being in the form of an electriccircuit of the non-arcing type, said circuit inin presence of eludinga plurality of resistor units' each active in thecompletion oi the circuit, each of" said units havin a formation to temperature values'mdivid'nal to itse f when positioned in its circuit-completing position, the'chamber walls being arranged to support the units in service position, and said chamber having a wall provided with openings for the passage of individual units to and from service position, the arrangement of the units relative to each other being such as to set up heatin conditions within the chamber determined y the arrangement of units relative to each other within the chamben,

21. Means as in claim 20 characterized in that the units are interchangeable to produce desired temperature conditions by the chamber.

In testimony whereof I aifix my signature two' witnesses:-.- ALF-RED RUCKSTAHLi Witnesses:

CHAS- W. S'inmman,

Mm'moir.

reduce 

